The present invention relates in general to remote keyless entry systems for motor vehicles, and, more specifically, to increasing transmission range between a vehicle base station and a handheld portable transceiver fob without exceeding regulatory average field strength limitations.
Remote keyless entry (RKE) systems for use with motor vehicles are well known in the art. Such systems typically include at least one remote control device, which typically takes the form of a key fob. The key fob includes a wireless transmitter for use by the vehicle owner or user to transmit wireless, usually radio frequency (RF), vehicle device function signals and includes a number of vehicle function buttons for use in transmitting such signals. A receiver and controller are typically provided in the vehicle for receiving the vehicle device function signals and controlling one or more vehicle devices in order to effect the desired vehicle function.
Vehicle devices which have been remotely controlled in such a fashion include door lock mechanisms, a vehicle trunk, interior and/or exterior vehicle lights, and a vehicle horn or other alarm. More recently, remote vehicle starting (sometimes together with remote temperature control) has been introduced. Prior RKE systems have typically utilized one-way transmissions from the portable fob to the vehicle. However, two-way communication systems are increasingly being used to facilitate user feedback for remote starting functions (e.g., reminders that a vehicle is running, and providing a remote indication of the vehicle temperature that has been achieved) and for providing guiding information as part of a vehicle locating system, for example. A two-way RICE system is shown, for example, in U.S. Pat. No. 6,724,322, entitled “Remote System For Providing Vehicle Information To A User,” issued to Tang et al. on Apr. 20, 2004, incorporated herein by reference.
A key fob must be small in size in order to facilitate carrying in a user's pocket or purse. Thus, miniaturized circuits and a small battery size are employed. Energy efficient microelectronic circuits and methods of operation are necessary in order to minimize battery consumption and maximize battery life. The key fob must also accommodate a transmit/receive antenna that is preferably hidden within the key fob because of esthetic and durability concerns. Therefore, the antenna gain that can normally be achieved is fairly low. The low antenna gain has constrained the operating range over which broadcasts between the portable fob and the vehicle base station can be reliably received.
One method to increase effective range would be to increase the transmitter power. However, government regulations aimed at reducing the likelihood of interference with other transmissions are in place which limit the allowed transmitter power. Prior art transmitters have operated near the regulatory limits and yet operating range has been less than desired for remote monitoring of a vehicle, such as when the vehicle has been remotely started.